This invention relates to a parachute system for a high speed aircraft and more particularly, but not by way of limitation, to a system for stabilizing an ejected aircraft seat and pilot or crew member during early deployment and delaying the opening of the main recovery parachute.
Ejection seats currently being used in high performance military aircraft are inherently unstable during free flight. In order to prevent excessive dynamic loads on the seat occupant after ejection, due to uncontrolled gyrations, the seat must be stabilized immediately after separation from the ejection guide rails in the aircraft. Present ejection seats deploy a drogue or pilot parachute to accomplish this stabilizing function and position the seat in a near upright attitude as the seat is decelerated to a low enough velocity for the recovery or main parachute to be deployed.
The pilot parachute also stabilizes the ejected seat as it descends from a high altitude to an altitude in the range of 15,000 feet at which time the main parachute is deployed. To prevent entanglement of the parachute, the pilot chute must be detached from the seat before the main parachute is inflated. There is a period of time between the release of the pilot chute and full deployment of the main chute during which the seat and the pilot combination has no stabilizing force applied thereto. Because of the inherent seat instability the seat will begin to tumble during this unrestrained period so that the seat could be in an adverse attitude at the time the main parachute opening shock is applied. If the parachute loads, which may be as high as 17 g's, are imposed on the pilot in a direction which is not approximately aligned with the spine serious injury can result. Therefore, it is important to be able to deploy the main parachute as rapidly as possible, certainly within 5 seconds from parachute deployment initiation to line stretch, in order to minimize the time during which the seat has no stabilizing force prior to main parachute opening shock.
Currently, aircraft ejection seats have a recovery system sequence which causes the pilot parachute to be detached from the ejected seat at 0.15 seconds after the main parachute deployment is initiated. The fixed time delay is intended to allow the main parachute deployment bag to reach a position just short of the pilot chute position before the pilot chute is detached. This delay is in order to avoid entanglement of the pilot chute and main chute, and still minimuze the unstabilized period between the pilot chute release and main parachute line stretch. Also, the main parachute can be deployed without first deploying the pilot chute in order to minimize the main chute's deployment time, but the seat attitude is uncontrolled and adverse attitude is likely.
Therefore, new aircraft ejection seat technology is now being developed which makes it possible to stabilize the seat with a controlled propulsion system for as long as 0.15 seconds after separation from the aircraft. This time period allows for a longer time for the pilot chute deployment. Ejection under high dynamic pressure conditions makes it desirable to delay the pilot chute deployment to avoid excessive seat deceleration which could be injurious to the seat occupant. Once the pilot chute is deployed, seat stability can be maintained aerodynamically. But, the problem of instability during the period of transition from the pilot chute to main parachute still exists since the propulsion attitude control system will already be exhausted by the time an accepted main parachute inflation velocity is reached. The subject invention provides a system and method for reducing the period of instability between the pilot chute release and main parachute line stretch and deployment.
In the following U.S. Pat. Nos. 3,027,126 to Wallace, 3,191,892 to Fuller et al, 3,861,625 to Sadler et al, 3,926,391 to Nordine, and 4,004,764 to Burklund et al, various types of aircraft parachute systems, parachute spreaders, and deployment systems are described. None of the prior art patents describe the unique system as described herein for providing early deployment seat stabilization and delaying the opening of the main parachute.